Age differences in short-term memory and cell loss in the cortex of the rat

Studies with human and animal subjects have indicated age declines in short-term memory and cell loss in the cortex. Cell loss has been estamated by descriptive nonautomated methods. Declines in short-term memory may be related to reduced learning, movtivation, motor capacity, or some combination of these factors. Passive-avoidance tests of memory minimize these factors. Direct correlational studies on learning and memory in relation to cell loss in the same subject are not feasible in man and they have not been reported previously in animals. The aims of this study were to examine age differences in learning and short-term passive-avoidance memory in relation to cell packing density in the visual cortex of the Fisher 344 rat. Cell counts were made with a computer-guided, automated, image-analyzing system (TAS, Leitz). The following observations were made: (1) significant age differences in 2- and 6-hour short-term passive-avoidance retention or memory between mature and senescent rats were related to nonsignificant age differences in original learning inferred from starting latencies, running time and running distance and (2) sd compared to mature rats were associated with significant differences in neuron but not glia-vascular cell density in area 17 in the presence of nonsignificant age differences in cortical depth and brain weight. Aims of further studies are to establish the role of cell loss from the hippocampus in loss of short-term spatial memory with age and to develop criteria for differential counting of small neurons, glia, endothelial cells and pericytes.